The present invention relates generally to flow control valves and more specifically to such valves which are designed to maintain a constant predetermined flow rate independent of fluctuations in inlet and/or outlet pressures.
A wide variety of applications exist wherein it is important to accurately control the rate of flow of a fluid. While such control is quite easily accomplished when the inlet and outlet pressures of the fluid are maintained constant, it is often not possible to achieve such a constant pressure condition. Thus, in these situations it is necessary for the flow regulator to incorporate means to automatically compensate for variations in either the inlet pressure or the outlet pressure or both.
This is typically accomplished by incorporating a variable orifice the size of which is controlled by an axially movable member having opposed pressure surfaces and spring biasing means operable such as to maintain a constant flow rate across the orifice. These valves must also incorporate a second orifice which has a permanently fixed area or a manually adjustably fixed orifice whereby the predetermined flow rate may be adjusted to the desired level.
While there exist many different types of valving arrangements operable to achieve constant adjustable preset flows, these valves are not totally satisfactory in that the pressure and flow rate ranges over which they are able to maintain a desired level of accuracy are relatively small hence necessitating manufacture and possible stocking of a substantially greater number of designs in order to accommodate the full range applications.
Additionally, in more recent times there have developed applications wherein it is desirable to incorporate flow control valving in connection with cleaning or purifying end product components. Such applications, commonly referred to as "ultra-pure", include portions of the electroncis industry wherein it is absolutely imperative that the cleaning fluid be devoid of even the smallest electrically conductive particle contamination and hence it is especially important to avoid any metal components within the flowpath through the valve. Other "ultra-pure" applications may be concerned with other forms of contamination such as bacteria growth for example. It is possible for such bacteria growth to occur in small pockets of low fluid turbulence within such valve structures even though the fluid is continuously flowing therethrough.
Additionally, virtually all flow control valves of which the applicant is aware have some degree of leakage across adjacent metering and/or moving surfaces. While this leakage may be minimized such as to become relatively insignificant with respect to relatively high flow rates, this leakage factor does become a significant error factor in valves used for relatively low flow rates.
The present invention, however, provides an improved adjustable flow control valve which is specifically designed to overcome the problems noted above and other disadvantages associated with prior designs. In one embodiment, a manually adjustably fixed orifice is positioned within the axially facing surface of the control piston thus not only enabling adjusting control of the flow rate but also providing for a change in surface area against which the pressure forces are acting. This arrangement serves to both significantly improve the accuracy of the control valves within the same typical ranges of existing valves as well as to provide comparable accuracy to that offered by conventional flow control valves over a substantially greater range. Also, the pressure compensating spring biasing means are remotely located outside of the fluid flowpath thus eliminating these elements as a potential source of contamination of fluid flowing therethrough. This embodiment is well suited for fabrication from various polymeric compositions or when intended for high pressure applications from suitable metal alloys.
Another embodiment of the present invention is also disclosed which is well suited for fabrication from suitable polymeric compositions. This embodiment is specifically designed to provide a substantially zero leakage flow control valve and incorporates a rolling diaphragm approach to achieve a positive seal between the various chambers. Because of the zero leakage, this embodiment affords extremely precise accurate fluid flow control particularly at very low flow rates where small leakages may create a significant error in total flow.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.